Prion diseases are fatal neurodegenerative diseases of humans and animals. Dissemination in the nervous system occurs by prion agent movement along nerve fibers and transynaptic spread between neurons. The long-term goal of the proposed research is to define the mechanism of prion agent transport in the nervous system. These events are central to understanding the pathogenesis of prion diseases, but the mechanism of prion dissemination within the nervous system is not well understood. In this application, in vivo and in vitro models will be used to investigate transynaptic and axonal transport of prions. The neuromuscular junction, a peripheral synapse, will be used to study transynaptic spread of prions between peripheral nerves and skeletal muscle cells in vivo, and in mixed neuron-muscle co-cultures in vitro. These studies can identify the role of the neuromuscular junction in the spread of the prion agent to peripheral tissues and provide an in vitro model to investigate cellular pathways involved in transneuronal spread in the nervous system. To investigate the pathway of prion movement in neurons, studies will investigate the spread of prions between the brain and nasal mucosa within olfactory receptor neurons. These studies can determine the role of the olfactory nerve in centrifugal prion spread to the nasal mucosa where agent shedding is a potential route of prion transmission.